一批书卖掉一半后又运来405本这时的书相当于原来书总数的5/6原来有多少本书

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  • 设原来有x本书

    依题意得:1/2x+405=5/6x

    5/6x-1/2x=405

    1/3x=405

    x=1215

    405÷(5/6-1/2)

    =405÷1/3

    =405×3

    =1215(本)

    答: